In Civilization V, the roads work a little differently than they do in the previous games. They are still constructed by Workers and allow units to move larger distances within a turn by negating the movement costs of terrain. However, they now have an upkeep cost: roads within your territory cost 1 Gold per tile per turn.

If a road is within a city's borders, the owner of the city pays for the maintenance of the road, regardless of which player built it. This allows for a potent exploit: sign an open borders treaty with an opponent, then build roads on every hex possible within his or her cultural borders. This will severely weaken your opponent's economy, since they will lose 1 Gold per turn per road hex. Running out of gold will slow your opponent's scientific progress and force military units to disband, making it difficult for the opponent to discover new technologies and maintain a defensive army without strengthening his or her economy first. Moreover, building roads will not cause diplomatic incidents with AI players, who may even propose to extend the open borders treaty.

Railroads make the aforementioned tactic twice as potent, thanks to their doubled maintenance cost. It can, however, be reduced by the Wagon TrainsSocial Policy from the Commerce tree, which halves maintenance costs for roads and railroads once the player picks it.

A road is a path between places suitable for wheeled traffic. The Romans were famous for the quality of their roads, and in fact many are still in use today - albeit with repairs and improvements made since.